Lithium-ion battery

ABSTRACT

A lithium-ion battery having a wound electrode configuration includes a wound cell element that includes a positive electrode and a negative electrode, the positive electrode including a current collector and a first active material and the negative electrode including a current collector and a second active material. The second active material has a potential that is greater than 0.2 volts versus a lithium reference electrode. The wound cell element includes a region where an edge of the positive electrode is provided proximate an edge of the negative electrode and the second active material near the edge of the negative electrode does not extend beyond the first active material near the edge of the positive electrode.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation-In-Part of and incorporates herein by reference each of the following patent applications in their entirety: U.S. patent application Ser. No. 10/978,712, filed Oct. 29, 2004 now U.S. Pat. No. 7,682,745); U.S. patent application Ser. No. 10/979,043, filed Oct. 29, 2004 now U.S. Pat. No. 7,807,299); U.S. patent application Ser. No. 10/979,040, filed Oct. 29, 2004 now U.S. Pat. No. 7,811,705); U.S. patent application Ser. No. 10/976,508, filed Oct. 29, 2004 now U.S. Pat. No. 7,337,010); and U.S. patent application Ser. No. 11/260,853, filed Oct. 27, 2005 know U.S. Pat. No. 7,635,541), which claims priority from U.S. Patent Provisional Application No. 60/624,075, filed Oct. 29, 2004 and U.S. Provisional Patent Application No. 60/647,292, filed Jan. 26, 2005.

BACKGROUND

The present invention relates generally to the field of lithium-ion batteries and methods of making such batteries.

Lithium-ion batteries or cells include one or more positive electrodes, one or more negative electrodes, and an electrolyte provided within a case or housing. Separators made from a porous polymer or other suitable material may also be provided intermediate or between the positive and negative electrodes to prevent direct contact between adjacent electrodes. The positive electrode includes a current collector (e.g., aluminum such as an aluminum foil) having an active material provided thereon (e.g., LiCoO₂), and the negative electrode includes a current collector (e.g., copper such as a copper foil) having an active material (e.g., a carbonaceous material such as graphite) provided thereon. The active materials for the positive and negative electrodes may be provided on one or both sides of the current collectors.

During charging and discharging of the battery, lithium ions move between the positive electrode and the negative electrode. For example, lithium ions flow from the negative electrode to the positive electrode during discharging of the battery, and in the opposite direction during charging.

One issue associated with conventional secondary (i.e., rechargeable) lithium-ion batteries is lithium plating. Lithium plating, which is a well-known phenomenon characterized by a buildup of lithium metal on the negative electrode, may occur when the potential of the negative electrode drops to 0.0 volts (V) versus Li/Li⁺. Lithium plating can result in decreased battery capacity, since the buildup of lithium on the negative electrode decreases the amount of cyclable lithium available in the battery. Internal battery shorts may also result from lithium plating, for example, when the buildup of lithium becomes so significant that dendrites form on the negative electrode and extend to and make contact with an adjacent positive electrode.

The issue of lithium plating is particularly problematic in batteries having negative active materials that exhibit relatively low potentials versus Li/Li⁺. Carbon-based active materials commonly used in lithium secondary batteries, for example, have an average potential of approximately 0.1 V versus Li/Li⁺.

To reduce the likelihood of lithium plating, battery manufacturers typically provide excess negative electrode capacity to balance the positive electrode capacity, particularly at relatively high-current regions of the negative electrodes (e.g., edges of the electrodes). The additional negative active material provides additional intercalation sites for the cyclable lithium originating with the positive active material.

One method of providing additional negative active material is to utilize negative electrodes that have different (e.g., larger) physical dimensions than the positive electrodes. Depending on the type of battery configuration involved (e.g., wound electrode, flat plate electrode, Z-fold electrode, etc.), the manner in which the dimensions of the negative electrode differ from that of the positive electrode may vary.

For example, in a flat plate lithium battery that includes a plurality of positive and negative electrodes, lithium plating may occur at relatively high current density regions (e.g., near the four edges of the negative electrodes). To compensate for this tendency, conventional batteries are designed such that the negative electrodes (or the active material provided thereon) extend beyond the ends of the positive electrodes (or the active material provided thereon) in all directions by an amount sufficient to compensate for variations in the winding/assembly process (e.g., by an amount up to 1 millimeter or more).

FIGS. 1-2 illustrate a portion of a battery 100 that includes a plurality of negative electrodes 110 (which include a current collector 112 and active material 114 provided thereon), a plurality of positive electrodes 120 (which include a current collector 122 and active material 124 provided thereon), and separators 130 and electrolyte between the positive and negative electrodes. Although shown as being coextensive with the active material 114 in FIG. 1, the separator(s) may be provided such that it extends beyond the edge of the adjacent electrode to prevent shorting between adjacent electrodes (i.e., the separator may extend above and below the edge of the active material 114 shown in FIG. 1). The portion of the active material 114 that extends beyond the positive electrodes 120 is thus used to compensate for the tendency to plate lithium. The extent to which the negative electrodes extend beyond the edges of the positive electrodes (shown by arrows A-A and B-B in FIG. 2) may be up to one millimeter (mm) or more.

A similar design rule is used in the context of wound (e.g., jellyroll style) lithium batteries, as shown in FIGS. 3-4. As illustrated, a wound electrode battery 200 includes a negative electrode 210 (which includes a current collector 212 and active material 214 provided thereon) and a positive electrode 220 (which includes a current collector 222 and active material 224 provided thereon). Separators 230 are provided between the positive and negative electrodes. As illustrated in FIGS. 3-4, the top and bottom edges of the negative electrode 210 extend beyond the edges of the positive electrode 220 by a distance C that may be up to one millimeter or more. Additionally, because a leading edge 211 of the negative electrode is also a potential location where plating might occur, the leading edge 211 of the negative electrode 210 extends a distance D (e.g., up to one millimeter or more) beyond a leading edge 221 of the positive electrode 220.

In cases where an accordion-style fold (also referred to as a “Z fold” or a “zigzag” fold) is used for the electrodes, multiple design rules may be employed to mitigate lithium plating. For example, the top and bottom edges of the negative electrodes may extend beyond those of the positive electrodes in a manner similar to that described above with respect to wound electrodes. Accordian-style folding of the electrodes also provides an additional area of potential concern, however. FIG. 5 illustrates a battery 300 having an electrode set 302 that is folded accordion-style. The electrode set 302 includes a negative electrode 310 (which includes a current collector 312 and active material 314 provided thereon), a separator 330, and a positive electrode 320 (which includes a current collector 322 and active material 324 provided thereon). Because of the manner in which the electrode set 302 is folded, at certain localized areas within the battery 300, there will be a greater amount of positive active material than negative active material. One such area is shown in FIG. 5, where the positive electrode 320 is outside the negative electrode 310 at a fold. Because there is more positive active material in this region than negative active material (owing to the larger radius, and hence greater surface area, of the positive electrode in this area), the negative active material would be unable to take in all of the cyclable lithium provided by the positive active material in this area unless steps are taken to mitigate against such a circumstance. As shown in FIG. 5, one possible solution is to mask the positive current collector 322 such that no positive active material 324 is provided in this region (denoted with reference numeral 326). One difficulty with such a solution is that it is relatively complicated to accurately mask regions on the electrodes to ensure that they will line up appropriately at locations of the folds.

Another potential solution for accordion-style folded electrodes is shown in FIG. 6, which shows a portion of a battery 400 having a folded negative electrode 410 (which includes a current collector 412 and active material 414 provided thereon) with positive electrode plates 420 (which includes a current collector 422 and active material 424 provided thereon). Separators 430 are provided between the positive and negative electrodes. By providing positive plates 420 interspersed within the folded electrode arrangement, there is additional negative active material near each of the rounded folded portions of the negative electrode 410 to take in any excess lithium from the positive active material 424.

Each of the various configurations described above suffers from various drawbacks. For example, each of the above-described configurations utilizes a larger negative electrode as compared to the positive electrode (with an associated amount of additional active material provided thereon), which increases the overall size of the battery and results in an increased materials cost. Additionally, each of these configurations requires careful alignment of the various components to ensure that the negative active material is properly positioned such that it will absorb excess lithium from the positive material, which complicates manufacturing processes and introduces increased labor and equipment costs. In certain cases, negative electrodes may be made even larger than are necessary to absorb the excess lithium in order to compensate for potential variability in manufacturing processes which may result in slight misalignments of the electrodes. Further still, the use of excess electrode area and active material results in batteries having lower energy density than might otherwise be obtained, since the excess electrode area does not fully contribute to the capacity of the battery.

SUMMARY

An exemplary embodiment relates to a lithium-ion battery having a wound electrode configuration includes a wound cell element that includes a positive electrode and a negative electrode, the positive electrode including a current collector and a first active material and the negative electrode including a current collector and a second active material. The second active material has a potential that is greater than 0.2 volts versus a lithium reference electrode. The wound cell element includes a region where an edge of the positive electrode is provided proximate an edge of the negative electrode and the second active material near the edge of the negative electrode does not extend beyond the first active material near the edge of the positive electrode.

Another exemplary embodiment relates a lithium-ion battery that includes a first electrode comprising a first current collector and a first active material and a second electrode comprising a second current collector and a second active material, the second active material having a potential that is greater than 0.2 volts versus a lithium reference electrode. The battery also includes a wound element having a central longitudinal axis and comprising the first electrode and the second electrode. The second active material is configured to resist lithium plating in the battery and does not extend beyond the first active material along the central longitudinal axis for at least a portion of the wound element.

Another exemplary embodiment relates to a lithium-ion battery that includes a positive electrode having a leading edge, a trailing edge, and first and second opposed lateral edges, the positive electrode comprising a current collector and a first active material. The battery also includes a negative electrode having a leading edge, a trailing edge, and first and second opposed lateral edges, the negative electrode comprising a current collector and a second active material comprising a lithium titanate material. The positive electrode and negative electrode are arranged to form a wound cell element such that the leading edges, trailing edges, and lateral edges of the positive and negative electrodes are generally aligned. The second active material does not extend beyond the first active material along at least a portion of an edge region in the wound cell element, the edge region comprising at least one of the aligned leading edges, the aligned trailing edges, the aligned first lateral edges, and the aligned second lateral edges of the positive and negative electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of a prior art lithium-ion battery having flat plate electrodes.

FIG. 2 is a cross-sectional view of the battery shown in FIG. 1 taken along line 2-2.

FIG. 3 is an isometric view of a portion of a prior art lithium-ion battery having wound electrodes.

FIG. 4 is a cross-sectional view of the battery shown in FIG. 3 taken along line 4-4.

FIG. 5 is a cross-sectional view of a prior art lithium-ion battery having accordion-style electrodes.

FIG. 6 is a cross-sectional view of a prior art lithium-ion battery having an accordion-style negative electrode with positive electrode plates interspersed between the folds of the negative electrode.

FIG. 7 is a cross-sectional view of a portion of a lithium-ion battery having flat plate electrodes according to an exemplary embodiment.

FIG. 8 is a perspective view of a portion of the battery shown in FIG. 7.

FIG. 9 is an isometric view of a lithium-ion battery having a wound electrode configuration according to an exemplary embodiment.

FIG. 10 is a cross-sectional view of a portion of the battery shown in FIG. 9.

FIG. 11 is a cross-sectional view of a lithium-ion battery having accordion-style electrodes.

FIG. 12 is a cross-sectional view of a portion of a lithium-ion battery according to an exemplary embodiment.

FIG. 13 is a cross-sectional view of a portion of a lithium-ion battery according to an exemplary embodiment.

FIG. 14 is a cross-sectional view of a portion of a lithium-ion battery according to an exemplary embodiment.

FIG. 15 is a cross-sectional view of a portion of a lithium-ion battery according to an exemplary embodiment.

FIG. 16 is a photograph showing a portion of a lithium-ion battery using a carbonaceous negative active material.

FIG. 17 is a photograph showing a portion of a lithium-ion battery using a lithium titanate negative active material.

FIG. 18 is a schematic view of an implantable medical device (IMD) provided within the body of a patient according to an exemplary embodiment.

FIG. 19 is a schematic view of another implantable medical device (IMD) provided within the body of a patient according to an exemplary embodiment.

FIG. 20 is a photograph showing a portion of a lithium-ion battery using a carbonaceous negative active material and employing a design rule in which the negative electrode extends beyond the positive electrode.

DETAILED DESCRIPTION

According to an exemplary embodiment, a lithium-ion battery utilizes a negative active material that is configured to provide enhanced flexibility in the physical design of the battery. For example, the use of certain materials may allow for the elimination of relatively complicated and expensive design rules which are intended to prevent lithium plating at the negative electrode. Various advantages may be obtained from eliminating such design rules, including, for example, better overall energy density for the batteries, simpler and more inexpensive manufacturing processes, material reduction and cost savings, and the like.

According to various exemplary embodiments as will be described in greater detail below, a lithium-ion battery includes a housing (e.g., a can, case, casing, etc.) in which one or more positive electrodes, one or more negative electrodes, and an electrolyte is provided. One or more separators made from a porous polymer or other suitable material may also be provided intermediate or between the positive and negative electrodes to prevent direct contact between adjacent electrodes. The positive and negative electrodes each include a current collector and an active material provided on one or more sides thereof.

According to an exemplary embodiment, the battery housing is made of stainless steel or another metal (e.g., titanium or titanium alloys, aluminum or aluminum alloys, etc.). According to other exemplary embodiments, the battery housing may be made of a plastic material or a plastic-foil laminate material (e.g., an aluminum foil provided intermediate a polyolefin layer and a polyester layer).

Any suitable electrolyte may be used depending on desired performance characteristics of the battery and other factors. According to various exemplary embodiments, the electrolyte may be a lithium salt dissolved in one or more non-aqueous solvents, a lithium salt dissolved in a polymeric material such as poly(ethylene oxide) or silicone, a solid state electrolyte such as a lithium-ion conducting glass, or an ionic liquid such as an N-methyl-N-alkylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt.

According to one exemplary embodiment, the electrolyte is a 3:7 mixture of ethylene carbonate to ethylmethyl carbonate (EC:EMC) in a 1.0 M salt of LiPF₆. According to another particular exemplary embodiment, the electrolyte includes a polypropylene carbonate solvent and a lithium bis-oxalatoborate salt (sometimes referred to as LiBOB). According to other exemplary embodiments, the electrolyte may comprise one or more of a PVDF copolymer, a PVDF-polyimide material, and organosilicon polymer, a thermal polymerization gel, a radiation cured acrylate, a particulate with polymer gel, an inorganic gel polymer electrolyte, an inorganic gel-polymer electrolyte, a PVDF gel, polyethylene oxide (PEO), a glass ceramic electrolyte, phosphate glasses, lithium conducting glasses, lithium conducting ceramics, and an inorganic ionic liquid or gel, among others.

According to an exemplary embodiment, the separator is a polymeric material such as a polypropylene/polyethelene copolymer or another polyolefin multilayer laminate that includes micropores formed therein to allow electrolyte and lithium ions to flow from one side of the separator to the other. The thickness of the separator is between approximately 10 micrometers (μm) and 50 μm according to an exemplary embodiment. According to a particular exemplary embodiment, the thickness of the separator is approximately 25 μm and the average pore size of the separator is between approximately 0.02 μm and 0.1 μm.

The positive electrode(s) include a current collector made of a conductive material such as a metal. According to an exemplary embodiment, the positive current collector is formed from aluminum or an aluminum alloy, and may be provided as a thin foil, a grid (e.g., a mesh grid, an expanded metal grid, a photochemically etched grid, etc.), or any other suitable configuration. The current collector may also have an electrically conductive member or element (e.g., a tab) coupled thereto and extending therefrom. The tab may be formed from aluminum or an aluminum alloy (or any other suitable material), and may serve as a terminal for the battery according to an exemplary embodiment.

The positive current collector has a layer of active material provided on one or both sides thereof. The active material layer provided on the positive current collector (hereinafter referred to as the “positive active material”) may be made up of a single active material or may include multiple active materials (either provided as separate layers or intermixed). The positive active material may also include a binder material that includes a material such as polyvinylidine fluoride (PVDF) and/or an elastomeric polymer such as styrene butadiene rubber (SBR) (carboxymethylcellulose may be provided by itself with a water solvent or may be provided in conjunction with the SBR). The positive active material may also include a conductive additive such as carbon black.

According to an exemplary embodiment, the positive active material is a material or compound that includes lithium that may be doped and undoped during discharging and charging of the battery. The positive active material may include any one or more of the following materials: lithium cobalt oxide (LiCoO₂); lithium manganese oxide (LiMn₂O₄); LiCo_(x)Ni_((1−x))O₂ (0.05≦x≦0.8); LiAl_(x)Co_(y)Ni_((1−x−y))O₂ (0.05≦x≦0.3, 0.1≦y≦0.3); LiM_(x)′M_(1−x)″O₂ (where M′ and M″ are metals such as Co, Ni, Mn, Fe, Cr, V, Zn, Al, Cd, and mixtures thereof); Li_(1−x)MO₂ (where M is a metal such as cobalt, nickel, or manganese and 0≦x≦0.5); LiM′_(x)M″_(1−x)PO₄ (where 0≦x≦1 and M′ and M″=Fe, Co, Ni, Mn, Cu, V. Ti, Cr, Zn, Cd, and mixtures thereof); and any other suitable active material such as those described in U.S. patent application Ser. No. 10/978,712 filed Oct. 29, 2004, the entire disclosure of which is incorporated herein by reference. According to a particular exemplary embodiment, the positive active material includes lithium cobalt oxide.

The thickness of the positive active material may differ according to various exemplary embodiments. According to one exemplary embodiment, the thickness of the positive active material is between approximately 0.1 μm and 3 mm. According to another exemplary embodiment, the thickness of the positive active material is between approximately 25 μm and 300 μm. According to a particular exemplary embodiment, the thickness of the positive active material is approximately 75 μm.

The negative electrode(s) includes a current collector made of a conductive material such as a metal. According to an exemplary embodiment, the negative current collector is formed from copper, titanium, nickel, aluminum, or alloys thereof, and may be provided as a thin foil, a grid (e.g., a mesh grid, an expanded metal grid, a photochemically etched grid, etc.), or any other suitable configuration. The negative current collector may also have an electrically conductive member or element (e.g., a tab) coupled thereto and extending therefrom. The tab may be formed from nickel or a nickel alloy, vanadium or a vanadium alloy, or any other suitable material, and may serve as a terminal for the battery according to an exemplary embodiment. According to a particular exemplary embodiment, the tab may couple the negative current collector to the battery housing.

The negative current collector has a layer of active material provided on one or both sides thereof. The active material layer provided on the negative current collector (hereinafter referred to as the “negative active material”) may be made up of a single active material or may include multiple active materials (either provided as separate layers or intermixed). The positive active material may also include a binder material (e.g., polyvinylidine fluoride (PVDF) or an elastomeric polymer) and/or a conductive additive such as carbon black, graphite, or a mixture thereof.

According to an exemplary embodiment, the negative active material is selected such that it has an average potential that is greater or equal to approximately 0.2 V versus Li/Li⁺ (e.g., according to one particular exemplary embodiment, the negative active material has an average potential that is greater or equal to approximately 0.3 V versus Li/Li⁺; according to a particularly preferred embodiment, the negative active material is a titanate material having an average potential that is greater or equal to approximately 1.5 V versus Li/Li⁺). The inventors have unexpectedly discovered that the use of negative electrode materials that possess a relatively high average potential versus Li/Li⁺ reduces the likelihood of lithium plating. According to one exemplary embodiment, such a negative active material is used in conjunction with a positive active material that has an average potential of greater than approximately 3 V versus Li/Li⁺ (e.g., LiCoO₂).

According to an exemplary embodiment, the negative active material is a lithium titanate material such as Li₄Ti₅O₁₂ (referred to alternatively as Li_(4/3)Ti_(5/3)O₄) having a spinel structure. Other lithium titanate materials which may be suitable for use as the negative active material may include one or more of the following lithium titanate materials: LiTi₂O₄, Li₂TiO₃, Li_(x)Ti_(y)O₄ (where 1.0≦x≦1.6 and 1.6≦y≦2.0), Li₄M_(x)Ti_(5−x)O₁₂ (where 0≦x≦1.0 and M is a metal such as vanadium, iron, aluminum, nickel, cobalt, copper, chromium, molybdenum, niobium or combinations thereof) and LiM′M″XO₄ (where M′ is a metal such as nickel, cobalt, iron, manganese, vanadium, copper, chromium, molybdenum, niobium, or combinations thereof, M″ is an optional three valent non-transition metal, and X is zirconium, titanium, or a combination of these two). Note that such lithium titanate materials may be used in any state of lithiation (e.g., Li_(4+x)Ti₅O₁₂, where 0≦x≦3).

One advantage of using a lithium titanate material instead of a carbonaceous material is that it is believed that the use of a lithium titanate material allows for charging and discharging of the battery at higher rates than is capable using carbonaceous materials. Lithium titanate materials are also believed to offer superior cycle life because they are so called “zero-strain” materials. Zero strain materials have crystal lattices which do not experience shrinkage or contraction with lithium doping/de-doping, making them free from strain-related degradation mechanisms.

Another advantageous feature of using a lithium titanate material is that it is believed that when used in a negative electrode of a lithium-ion battery, such materials will cycle lithium at a potential plateau of about 1.5 V versus a lithium reference electrode. This is substantially higher than graphitic carbon, which is traditionally used in lithium ion batteries, and cycles lithium down to about 0.1 V in the fully charged state. As a result, the battery using lithium titanate is believed to be less likely to result in lithium plating during charging.

Being free from the risk lithium plating, cells with lithium titanate negative electrodes may also be charged at rates that exceed those with carbon negative electrodes. For example, a common upper limit for the rate of charge in lithium ion batteries is about 1 C (meaning that the battery can be fully charged from the discharged state in one hour). Conversely, it has been reported in literature that lithium titanate may be charged at rates up to 10 C (i.e., attaining full charge in 1/10 hour, or six minutes). Being able to recharge a battery more quickly substantially increases the functionality of devices that employ such a battery. A further advantage of the higher potential of the lithium titanate material is that it avoids decomposition of organic solvents (such as propylene carbonate) commonly used in lithium ion batteries. In so doing, it may reduce negative consequences such as formation of gas, cell swelling, reduction of reversible battery capacity, and buildup of resistive films which reduce battery power.

Other materials having cycling potentials that exceed that of lithium by several hundred millivolts and which may be suitable for use as the negative active material include the materials listed in Table 1. Such materials may be used alone or in combination with the lithium titanates described above and/or any of the other materials listed in Table 1.

TABLE 1 Cycling Potentials (vs Li) Class Compound Vmin Vmax Vavg Oxides TiO₂ (Anatase) 1.4 2 1.80 Oxides WO₂ 0.6 1.3 0.80 Oxides WO₃ 0.5 2.6 1.0 Oxides MoO₂ 1.3 2 1.60 Oxides Nb₂O₅ 1.0 2 1.50 Oxides LiWO₂ 0.75 Oxides Li_(x)MoO₂ 0.8 2 1.60 Oxides V₆O₁₃ 2.30 Oxides Li₆Fe₂O₃ 0.75 Oxides LiFeO₂ 1.0 3.0 2.0 Oxides Fe₂O₃ 0.2 2.0 0.75 Oxides MO where M = Co, Ni, Cu or Fe 0.8-1.5 Sulfides FeS₂ 1.3 1.9 1.65 Sulfides MoS₂ 1.75 Sulfides TiS₂ 2.00 Alloys Sn—Bi 0.75 Alloys Alloys comprising of Al, Si or Sn 0.30 and other elements Alloys Sn—Co—C 0.30 Alloys Sb 0.90 Alloys NbSe₃ 1.95 Alloys Bi 0.80 Alloys In 0.60 Alloys LixAl 0.36 Alloys LixSn 0 1.3 0.50 Alloys Sn—Sb 0.0-1.0 Polymers Poly(phenylquinoline) 1.50 Polymers Polyparaphenylene 0.70 Polymers Polyacetylene 1.00 Vanadates Li_(x)MVO₄ where M = Ni, Co, 2.0-0.5 Cd, Zn

According to a particular exemplary embodiment, a negative active material such as Li₄Ti₅O₁₂ is coated on an aluminum foil using a conductive carbon filler and a PVDF, NMP (Polyvinylidene fluoride, N-methylpyrrolidone) binder solution. The binder may also include (in addition to or in place of the foregoing materials) an elastomeric polymer such as styrene butadiene rubber (SBR) (carboxymethylcellulose may be provided by itself with a water solvent or may be provided in conjunction with the SBR). The negative electrode coatings are made using the negative electrode material, the conductive carbon and the binder solution.

According to various exemplary embodiments, the thickness of the negative active material is between approximately 0.1 μm and 3 mm. According to other exemplary embodiments, the thickness of the active material may be between approximately 25 μm and 300 μm. According to another exemplary embodiment, the thickness of the active material may be between approximately 20 μm and 90 μm, and according to a particular exemplary embodiment, approximately 75 μm.

According to an exemplary embodiment, negative active materials such as those described above may allow for more flexible design rules to be employed in the design and manufacture of lithium-ion batteries. For example, because the use of a lithium titanate material reduces the risk of lithium plating at the negative electrode, lithium-ion battery designs may be modified such that the edges of the negative electrodes need not extend beyond the edges of the positive electrodes at all locations within the battery. This in turn allows for a reduction in negative electrode area (relative to the positive electrode area) and potentially improved energy density, while still providing protection against lithium plating.

It should be understood by those reviewing the present application that with respect to the various exemplary embodiments described herein, it is contemplated by the inventors that the need to provide excess negative active material in high current regions (e.g., edges of electrodes) may be eliminated using higher potential negative active materials. Where references are made to providing negative electrodes that have electrode edges that are coextensive (or which do not extend as far as) the adjacent edges of the positive electrodes, it should also be understood that similar advantages may be obtained by providing negative electrodes having negative active materials that are coextensive (or which does not extend as far as) the positive active material on the adjacent positive electrode (e.g., where the negative active material and/or positive active material are not coated to the edge of their respective electrodes). Examples of such configurations are provided in FIGS. 12-15 and described below. Further, because there is necessarily some variability in the battery assembly process that may cause electrodes to shift during the assembly process relative to each other, references to negative electrodes and/or negative active materials not extending as far as the positive electrodes and/or positive active materials should be interpreted to mean that the negative electrodes and/or negative active materials do not extend as far as the positive electrodes and/or positive active materials for all or a portion of the relevant area (e.g., a statement that the negative active material does not extend as far as the positive active material toward the top edge of a wound cell element should be interpreted to mean that the negative active material does not extend as far as the positive active material along at least a portion of the top edge of the wound cell element).

For example, FIG. 7 is a cross-sectional view of a portion of a lithium-ion battery 500 having flat plate electrodes having a generally rectangular (e.g., a square) geometry according to an exemplary embodiment, and FIG. 8 is a perspective view of a portion of the battery 500. The battery 500 includes a housing or casing 502 (e.g., a can) that may be made of any suitable material as described above. The battery 500 includes a plurality of generally planar negative electrodes 510 and positive electrodes 520, with separators 530 provided between the positive and negative electrodes. The negative electrodes 510 include current collectors 512 and an active material 514 provided on one or both sides thereof, and the positive electrodes 520 include current collectors 522 and an active material 524 provided on one or both sides thereof. Although illustrated as having a generally rectangular planar configuration, according to other exemplary embodiments, the electrodes may be circular or may have other suitable shapes.

As illustrated in FIGS. 7-8, the negative electrodes 510 do not extend beyond the edges of the positive electrodes 520 along their outer perimeter (as they do, for instance, in the batteries illustrated in FIGS. 1-2). According to an exemplary embodiment, the negative electrodes 510 have the same area as the positive electrodes 520 (i.e., the top, bottom, and side edges are coextensive or coterminous) and the active materials 514, 524 on both the negative electrodes 510 and positive electrodes 520 extend to the ends of their respective current collectors 512, 522. According to one exemplary embodiment, the active material provided on the negative electrode does not extend beyond the active material provided on the positive electrode near at least one of the edges of the electrodes. According to another exemplary embodiment, the area of the active material provided on the negative electrode is less than or equal to the area of the active material provided on the positive electrode.

FIGS. 9-10 illustrate a lithium-ion battery 600 having a wound electrode configuration according to an exemplary embodiment. The battery 600 includes a housing or casing 602 (e.g., a can) in which the wound cell element 604 is provided during assembly. As shown in FIG. 9, the element 604 is partially unwound to illustrate the components of the element.

The battery 600 includes a negative electrode 610 and positive electrode 620, with separators 630 provided between the positive and negative electrodes (according to an exemplary embodiment, two separators are utilized so that when the electrodes are wound, the positive and negative electrodes do not come into direct contact at any point, which may result in battery shorting). The negative electrode 610 includes a current collector 612 and an active material 614 provided thereon, and the positive electrode 620 includes a current collector 622 and an active material 624 provided thereon.

It should be noted that while the exemplary embodiment shown in FIG. 9 illustrates a battery in which the electrodes are wound to form a generally cylindrical cell element, other configurations may also be possible for wound or wrapped electrode batteries. For example, the shape of the cell element may be that of an oval or elongated flattened winding (e.g., having a generally rectangular winding with rounded corners) according to other exemplary embodiments. A mandrel or other structure may be used to define the shape which the cell element may take (e.g., by wrapping the electrodes around the mandrel).

As shown in FIGS. 9-10, the height of the negative and positive electrodes are substantially equal. That is, the top and bottom edges of the negative electrode 610 do not extend beyond the top and bottom edges of the positive electrode 620. According to an exemplary embodiment, the top and bottom edges of the positive and negative electrodes are coextensive or coterminous. As also shown in FIGS. 9-10, the leading edges 621, 611 of the positive and negative electrodes are substantially coextensive or coterminous (i.e., the leading edge 611 of the negative electrode 610 does not extend beyond that of the positive electrode 620).

FIG. 11 is a cross-sectional view of a lithium-ion battery 700 having an accordion-style electrode configuration (also referred to as a “Z fold” or a “zigzag” fold configuration) according to an exemplary embodiment. The battery 700 includes a housing or casing 702 (e.g., a can) in which a folded electrode set 704 is provided during assembly.

The battery 700 includes a negative electrode 710 and positive electrode 720, with a separator 730 provided between the positive and negative electrodes. The negative electrode 710 includes a current collector 712 and an active material 714 provided on one or both sides thereof, and the positive electrode 720 includes a current collector 722 and an active material 724 provided on one or both sides thereof.

As illustrated in FIG. 11, the positive active material 724 may be applied along substantially the entire length of the positive electrode 720, without the need to mask a portion of the current collector 720 in the region 726 (see, e.g., FIG. 5, in which a portion of the current collector 322 is not coated with active material in a region 326). Additionally, the top and bottom edges of the positive electrode 720 and negative electrode 710 may be coextensive or coterminous (i.e., instead of the edge of the negative electrode 710 extending beyond that of the positive electrode).

While FIGS. 7-11 illustrate exemplary embodiments in which the edges of the positive and negative electrodes are substantially coextensive or coterminous, those reviewing this disclosure will appreciate that other possibilities may be possible. FIGS. 12-15 illustrate portions of lithium-ion batteries according to various other exemplary embodiments. It should be understood that the embodiments illustrated in FIGS. 12-15 may be applied to batteries of any of a variety of configurations (e.g., flat plate electrode, wound electrode, Z-fold electrode, etc.). To this end, the edges of the various electrodes shown in FIGS. 12-15 may be applied to top and bottom edges of electrodes, leading and trailing edges of wound batteries, and the like.

FIG. 12 is a cross-sectional view of a portion of a lithium-ion battery 800 that includes a negative electrodes 810, a positive electrode 820, and a separator 830 provided between the positive and negative electrodes. The negative electrode 810 includes a current collector 812 and an active material 814 provided thereon, and the positive electrode 820 includes a current collector 822 and an active material 824 provided thereon. As shown in FIG. 12, the edge of the positive electrode 820 extends beyond the edge of the negative electrode 810. According to an exemplary embodiment, the positive electrode 820 may extend beyond the edge of the negative electrode 810 by between approximately 0 and 5 millimeters.

FIG. 13 is a cross-sectional view of a portion of a lithium-ion battery 900 that includes a negative electrode 910, a positive electrode 920, and a separator 930 provided between the positive and negative electrodes. The negative electrode 910 includes a current collector 912 and an active material 914 provided thereon, and the positive electrode 920 includes a current collector 922 and an active material 924 provided thereon. As shown in FIG. 13, the edge of the negative current collector 912 is coextensive or coterminous with the edge of the positive electrode 920, while the negative active material 914 terminates before the edge of the negative current collector 912. According to an exemplary embodiment, the negative active material 914 terminates between approximately 0 and 5 millimeters before the edge of the negative current collector 912. Because it is the negative active material 914 that is responsible for intercalating lithium, it is thus possible to use negative current collectors that have the same dimensions as the positive current collectors while using less active material by not coating the negative material all the way to its edge. The amount of negative active material (e.g., the amount by which the active material terminates before the edge of the current collector) may be selected so that there is an adequate or optimal amount of negative active material to intercalate the active lithium in the battery without resulting in lithium plating at the edges of the electrodes.

FIG. 14 is a cross-sectional view of a portion of a lithium-ion battery 1000 that includes a negative electrodes 1010, a positive electrode 1020, and a separator 1030 provided between the positive and negative electrodes. The negative electrode 1010 includes a current collector 1012 and an active material 1014 provided thereon, and the positive electrode 1020 includes a current collector 1022 and an active material 1024 provided thereon. As shown in FIG. 14, the negative active material 1014 does not extend to the edge of the negative current collector 1012 but is substantially coextensive or coterminous with the positive electrode 1020 and the positive active material 1024 provided thereon. According to an exemplary embodiment, the negative active material 1014 terminates between approximately 0 and 5 millimeters before the edge of the negative current collector 1012. The amount of negative active material (e.g., the amount by which the active material terminates before the edge of the current collector) may be selected so that there is an adequate or optimal amount of negative active material to intercalate the active lithium in the battery without resulting in lithium plating at the edges of the electrodes.

FIG. 15 is a cross-sectional view of a portion of a lithium-ion battery 1100 that includes a negative electrodes 1110, a positive electrode 1120, and a separator 1130 provided between the positive and negative electrodes. The negative electrode 1110 includes a current collector 1112 and an active material 1114 provided thereon, and the positive electrode 1120 includes a current collector 1122 and an active material 1124 provided thereon. As shown in FIG. 15, the negative current collector 1112 extends beyond the edge of the positive electrode 1120. The negative active material 1114 does not extend to the edge of the negative current collector 1112, and also does not extend such that it is coextensive or coterminous with the positive electrode 1120 and the active material 1124 provided thereon. According to an exemplary embodiment, the negative active material 1114 terminates between approximately 0 and 5 millimeters before the edge of the negative current collector 1112. The amount of negative active material (e.g., the amount by which the active material terminates before the edge of the current collector) may be selected so that there is an adequate or optimal amount of negative active material to intercalate the active lithium in the battery without resulting in lithium plating at the edges of the electrodes.

FIGS. 16-17 illustrate one advantage of using negative active materials such as those described above (e.g., lithium titanate active materials). FIG. 16 is a photograph showing the edge of a lithium-ion battery in which a carbonaceous negative active material that included mesocarbon microbeads was used on the negative current collector. In the example shown in FIG. 16, the edge of the negative electrode did not extend beyond the edge of the positive electrode (i.e., their edges were coextensive or coterminous). Extended battery cycling was performed, after which the battery was cut apart and viewed. As shown by the bright spots on the edges of the negative electrodes in FIG. 16, relatively severe lithium plating occurred during cycling of the battery. Notably, if the lithium-ion battery with a carbonaceous negative active material is built following the design rule that the negative electrode must extend beyond the positive electrode (e.g., by up to approximately 1 millimeter or more), lithium plating will generally not occur, as illustrated in FIG. 20.

The battery shown in FIG. 17, in contrast to that shown in FIG. 16, utilized a lithium titanate (Li₄Ti₅O₁₂) active material on the negative electrode. Similar to the battery shown in FIG. 16, the edges of the negative electrode were coextensive or coterminous with those of the positive electrode. The battery was then subjected to extended cycling (100 cycles at an accelerated charge discharge rate). As shown in FIG. 17, no lithium plating is readily apparent at the edges of the negative electrodes.

As described above, one advantageous feature associated with the use of negative active materials that have potentials that greatly exceed that of carbon (e.g., lithium titanate materials) is that design rules requiring that the negative active material extend beyond the positive active material by up to one millimeter or more may be eliminated. The inventors have discovered that the use of such high potential materials may also allow the production of batteries in which the positive active material and/or positive electrode may extend beyond the negative active material and/or negative electrode by several millimeters without resulting in lithium plating (e.g., up to 10 millimeters in some cases). This provides enhanced flexibility in the design of lithium-based batteries in addition to allowing for variability in the manufacturing/assembly process (e.g., in the past, negative electrodes had to extend beyond the positive electrodes to compensate for potential misalignment between the electrodes that may result in lithium plating; the use of higher potential materials may eliminate the need to compensate for such variability).

The batteries described herein may find utility in a variety of applications, including in implantable medical devices (IMDs). FIG. 18 illustrates a schematic view of a system 1200 (e.g., an implantable medical device) implanted within a body or torso 1232 of a patient 1230. The system 1200 includes a device 1210 in the form of an implantable medical device that for purposes of illustration is shown as a defibrillator configured to provide a therapeutic high voltage (e.g., 700 volt) treatment for the patient 1230.

The device 1210 includes a container or housing 1214 that is hermetically sealed and biologically inert according to an exemplary embodiment. The container may be made of a conductive material. One or more leads 1216 electrically connect the device 1210 and to the patient's heart 1220 via a vein 1222. Electrodes 1217 are provided to sense cardiac activity and/or provide an electrical potential to the heart 1220. At least a portion of the leads 1216 (e.g., an end portion of the leads shown as exposed electrodes 1217) may be provided adjacent or in contact with one or more of a ventricle and an atrium of the heart 1220.

The device 1210 includes a battery 1240 provided therein to provide power for the device 1210. The size and capacity of the battery 1240 may be chosen based on a number of factors, including the amount of charge required for a given patient's physical or medical characteristics, the size or configuration of the device, and any of a variety of other factors. According to an exemplary embodiment, the battery is a 5 mAh battery. According to another exemplary embodiment, the battery is a 300 mAh battery. According to various other exemplary embodiments, the battery may have a capacity of between approximately 1 and 1000 mAh.

According to other exemplary embodiments, more than one battery may be provided to power the device 1210. In such exemplary embodiments, the batteries may have the same capacity or one or more of the batteries may have a higher or lower capacity than the other battery or batteries. For example, according to an exemplary embodiment, one of the batteries may have a capacity of approximately 500 mAh while another of the batteries may have a capacity of approximately 75 mAh.

According to an exemplary embodiment, the battery may be configured such that it may be charged and recharged using an inductive charging system in which a primary or external coil is provided at an exterior surface of a portion of the body (either proximate or some distance away from the battery) and a secondary or internal coil is provided below the skin adjacent the primary coil.

According to another exemplary embodiment shown in FIG. 19, an implantable neurological stimulation device 1300 (an implantable neuro stimulator or INS) may include a battery 1302 such as those described above with respect to the various exemplary embodiments. Examples of some neuro stimulation products and related components are shown and described in a brochure titled “Implantable Neurostimulation Systems” available from Medtronic, Inc.

An INS generates one or more electrical stimulation signals that are used to influence the human nervous system or organs. Electrical contacts carried on the distal end of a lead are placed at the desired stimulation site such as the spine or brain and the proximal end of the lead is connected to the INS. The INS is then surgically implanted into an individual such as into a subcutaneous pocket in the abdomen, pectoral region, or upper buttocks area. A clinician programs the INS with a therapy using a programmer. The therapy configures parameters of the stimulation signal for the specific patient's therapy. An INS can be used to treat conditions such as pain, incontinence, movement disorders such as epilepsy and Parkinson's disease, and sleep apnea. Additional therapies appear promising to treat a variety of physiological, psychological, and emotional conditions. Before an INS is implanted to deliver a therapy, an external screener that replicates some or all of the INS functions is typically connected to the patient to evaluate the efficacy of the proposed therapy.

The INS 1300 includes a lead extension 1322 and a stimulation lead 1324. The stimulation lead 1324 is one or more insulated electrical conductors with a connector 1332 on the proximal end and electrical contacts (not shown) on the distal end. Some stimulation leads are designed to be inserted into a patient percutaneously, such as the Model 3487A Pisces-Quad® lead available from Medtronic, Inc. of Minneapolis Minn., and stimulation some leads are designed to be surgically implanted, such as the Model 3998 Specify® lead also available from Medtronic.

Although the lead connector 1332 can be connected directly to the INS 1300 (e.g., at a point 1336), typically the lead connector 1332 is connected to a lead extension 1322. The lead extension 1322, such as a Model 7495 available from Medtronic, is then connected to the INS 1300.

Implantation of an INS 1300 typically begins with implantation of at least one stimulation lead 1324, usually while the patient is under a local anesthetic. The stimulation lead 1324 can either be percutaneously or surgically implanted. Once the stimulation lead 1324 has been implanted and positioned, the stimulation lead's 1324 distal end is typically anchored into position to minimize movement of the stimulation lead 1324 after implantation. The stimulation lead's 1324 proximal end can be configured to connect to a lead extension 1322.

The INS 1300 is programmed with a therapy and the therapy is often modified to optimize the therapy for the patient (i.e., the INS may be programmed with a plurality of programs or therapies such that an appropriate therapy may be administered in a given situation).

A physician programmer and a patient programmer (not shown) may also be provided to allow a physician or a patient to control the administration of various therapies. A physician programmer, also known as a console programmer, uses telemetry to communicate with the implanted INS 1300, so a clinician can program and manage a patient's therapy stored in the INS 1300, troubleshoot the patient's INS system, and/or collect data. An example of a physician programmer is a Model 7432 Console Programmer available from Medtronic. A patient programmer also uses telemetry to communicate with the INS 1300, so the patient can manage some aspects of her therapy as defined by the clinician. An example of a patient programmer is a Model 7434 Itrel® 3 EZ Patient Programmer available from Medtronic.

According to an exemplary embodiment, a battery provided as part of the INS 1300 may be configured such that it may be charged and recharged using an inductive charging system in which a primary or external coil is provided at an exterior surface of a portion of the body (either proximate or some distance away from the battery) and a secondary or internal coil is provided below the skin adjacent the primary coil.

While the medical devices described herein (e.g., systems 1200 and 1300) are shown and described as a defibrillator and a neurological stimulation device, it should be appreciated that other types of implantable medical devices may be utilized according to other exemplary embodiments, such as pacemakers, cardioverters, cardiac contractility modules, drug administering devices, diagnostic recorders, cochlear implants, and the like for alleviating the adverse effects of various health ailments.

It is also contemplated that the medical devices described herein may be charged or recharged when the medical device is implanted within a patient. That is, according to an exemplary embodiment, there is no need to disconnect or remove the medical device from the patient in order to charge or recharge the medical device.

It should be noted that references to “front,” “back,” “upper,” and “lower” in this description are merely used to identify various elements as are oriented in the FIGURES, with “front” and “back” being relative the vehicle in which the battery assembly is placed.

For the purpose of this disclosure, the term “coupled” means the joining of two members directly or indirectly to one another. Such joining may be stationary in nature or moveable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or may be removable or releasable in nature.

It is also important to note that the construction and arrangement of the batteries and cells as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments of the present inventions have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present inventions as expressed in the appended claims. 

What is claimed is:
 1. A lithium-ion battery having a wound electrode configuration comprising: a wound cell element comprising a positive electrode and a negative electrode, the positive electrode comprising a current collector and a first active material and the negative electrode comprising a current collector and a second active material, wherein the current collectors of the positive and negative electrodes each include a leading edge, a trailing edge, and two lateral edges; wherein the second active material is a lithium titanate material; wherein the first active material is configured to be doped and undoped with lithium cations during cycling of the battery; wherein the current collector of the negative electrode comprises aluminum; and wherein the wound cell element comprises a region where a first lateral edge of the positive electrode is provided proximate a first lateral edge of the negative electrode and the first active material near the first lateral edge of the positive electrode extends beyond the second active material near the first lateral edge of the negative electrode in an axial direction relative to the wound cell element.
 2. The lithium-ion battery of claim 1, wherein the second active material has a potential that is approximately 1.5 volts versus a lithium reference electrode.
 3. The lithium-ion battery of claim 1, wherein the lithium titanate material is Li₄Ti₅O₁₂.
 4. The lithium-ion battery of claim 1, wherein the lithium titanate material is selected from the group consisting of LiTi₂O₄, Li₂TiO₃, Li_(x)Ti_(y)O₄, and combinations thereof.
 5. The lithium-ion battery of claim 1, wherein the second active material extends to the first lateral edge of the negative electrode and the first active material extends to the first lateral edge of the positive electrode.
 6. The lithium-ion battery of claim 1, wherein the wound cell element is generally cylindrical and the region is a top or bottom of the generally cylindrical wound cell element.
 7. The lithium-ion battery of claim 1, wherein the wound cell element has a central longitudinal axis and the second active material does not extend beyond the first active material in the longitudinal direction for at least a portion of the wound cell element.
 8. The lithium-ion battery of claim 1, wherein the first active material is LiCoO₂.
 9. The lithium-ion battery of claim 1, wherein the battery is installed in an implantable medical device.
 10. The lithium-ion battery of claim 1, wherein the first active material near the first lateral edge of the positive electrode extends beyond the second active material along an entire length of the first lateral edge of the negative electrode in an axial direction relative to the wound cell element.
 11. A lithium-ion battery comprising: a wound element comprising a first electrode and a second electrode, wherein the first electrode comprises a first current collector and a first active material and the second electrode comprises a second current collector and a second active material; wherein the second active material is selected from the group consisting of TiO₂, MoO₂, Nb₂O₅, V₆O₁₃, Li₆Fe₂O₃, and combinations thereof; wherein the second current collector comprises aluminum; wherein the first and second current collectors each include a leading edge, a trailing edge, and two lateral edges; wherein the first active material is configured to be doped and undoped with lithium cations during cycling of the battery; wherein the wound cell element comprises a region where a first lateral edge of the first electrode is provided proximate a first lateral edge of the second electrode and the first active material near the first lateral edge of the first electrode extends beyond the second active material in an axial direction relative to the wound cell element near the first lateral edge of the second electrode for at least a portion of the wound element; and wherein the first electrode is a positive electrode and the second electrode is a negative electrode.
 12. The lithium-ion battery of claim 11, wherein the second active material has a potential that is approximately 1.5 volts versus a lithium reference electrode.
 13. The lithium-ion battery of claim 11, wherein the current collector of the second electrode does not extend beyond the current collector of the first electrode in the longitudinal direction for at least a portion of the wound element.
 14. The lithium-ion battery of claim 11, wherein the wound element has a generally cylindrical shape.
 15. The lithium-ion battery of claim 11, wherein the first electrode and the second electrode each include a leading edge, and the first active material extends beyond the second active material for at least a portion of the leading edges.
 16. The lithium-ion battery of claim 11, wherein the first electrode and the second electrode each include a trailing edge, and the first active material extends beyond the second active material for at least a portion of the trailing edges.
 17. The lithium-ion battery of claim 11, wherein the first active material is LiCoO₂.
 18. The lithium-ion battery of claim 11, wherein the battery is installed in an implantable medical device.
 19. The lithium-ion battery of claim 11, wherein the first active material near the first lateral edge of the first electrode extends beyond the second active material in an axial direction relative to the wound cell element along an entire length of the first lateral edge of the negative electrode.
 20. A lithium-ion battery comprising: a wound cell element comprising a positive electrode and a negative electrode the positive electrode comprising a current collector and a first active material and the negative electrode comprising a current collector and a second active material, the second active material having a potential that is greater than approximately 1.0 V versus a lithium reference electrode; wherein the current collector of the negative electrode comprises aluminum; wherein the first active material is capable of being doped and undoped with lithium cations during cycling of the battery; wherein the positive electrode has a leading edge, a trailing edge, and first and second opposed lateral edges; and wherein the negative electrode has a leading edge, a trailing edge, and first and second opposed lateral edges; wherein the positive electrode and negative electrode are arranged such that the leading edges, trailing edges, and lateral edges of the positive and negative electrodes are generally aligned; and wherein the first active material extends beyond the second active material in an axial direction relative to the wound cell element along at least a portion of an edge region in the wound cell element, the edge region comprising at least one of the aligned first lateral edges and the aligned second lateral edges of the positive and negative electrodes.
 21. The lithium-ion battery of claim 20, wherein the second active material has an average potential that is greater than approximately 1.5 volts versus a lithium reference electrode.
 22. The lithium-ion battery of claim 20, wherein the second active material does not extend to the edge of the negative electrode along at least a portion of the edge region of the wound cell element.
 23. The lithium-ion battery of claim 22, wherein the first active material extends beyond the second active material along a central longitudinal axis of the wound cell element.
 24. The lithium-ion battery of claim 20, wherein the first active material is LiCoO₂.
 25. The lithium-ion battery of claim 20, wherein the battery is installed in an implantable medical device.
 26. The lithium-ion battery of claim 20, wherein the first active material extends beyond the second active material in an axial direction relative to the wound cell element along an entire length of one of the lateral edges of the negative electrode. 